When performing branching, distribution, etc. on optical fibers, the end portion of each optical fiber is exposed by removing the coating by a predetermined length; after fusion—splice the end portions to each other, the coating peeled-off portion (the portion requiring coating forming: coating formation portion) is protected by reinforcing through re-coating with UV curable resin. In some cases, the outer periphery of the optical fiber core is newly coated.
For re-coating, a coating forming device equipped with a mold is used. The mold is composed of a lower mold and an upper mold mounted thereto so as to be capable of being opened and closed. In the opposing surfaces (joint surfaces) of the lower and upper molds, there are formed semi-cylindrical re-coating grooves (molding grooves); when the upper mold is closed to be superimposed on the lower mold, their re-coating grooves are opposed to each other to define a cylindrical molding portion. The coating formation portion of an optical fiber is placed in this molding portion and then ultraviolet (UV) curable resin is supplied to the interior of the molding portion; when UV light is irradiated to the UV curable resin from outside the mold, the UV curable resin cures to re-coat the outer periphery of the coating formation portion.
From the viewpoint of convenience in accommodation, handling, etc., it is desirable that the coated portion be as small as possible. In view of this, nowadays, only the coating formation portion is re-coated with UV curable resin. Further, regarding re-coating, there are the following requirements:
1. With the development of Wavelength Division Mutiplexing (WDM) communication technology etc., there is a demand for production of optical fiber amplifiers and optical parts in a large amount, so that it is necessary to reduce the requisite processing time for the operations, such as optical fiber cutting, peeling-off of coating, connection of optical fibers, and coating of coating formation portions.
2. Since more and more coating forming devices have come to be used where optical parts are produced, there is a demand for a reduction in size, weight, and power consumption for convenience in handling. For a reduction in size and weight, the UV light utilization efficiency should be enhanced.
The above coating forming device makes it possible to coat the coating formation portion of an optical fiber with resin. However, it involves the following problems:
(1) The UV light irradiated to the mold is irradiated not only to the molding portion but also to its periphery. More specifically, the UV light is also irradiated to the joint surfaces between the lower and upper molds, the supply passage for supplying UV curable resin to the molding portion, the supply port connecting the supply passage and the molding portion, etc. Thus, when the UV curable resin supplied into the molding portion is allowed to protrude over the joint surfaces, the resin will cure between the joint surfaces, resulting in difficulty in opening the upper mold or generation of burr in the coated portion. Further, when some UV curable resin remains in the supply passage and the supply port, the resin will cure to clog the supply passage and the supply port.
(2) In actual coating operation, there may be a case where sufficient quantity of UV light does not reach the back side of the coating formation portion of the optical fiber placed in the mold. In such a case, the UV light irradiation time is increased or UV curable resin with thermosetting property is used, heating the resin with a heater while irradiating UV light thereto. However, increasing the UV light irradiation time makes it impossible to achieve a reduction in the time consumed for the coating operation. Consequently, it involves larger power consumption of the heater, according to the irradiation time increase, resulting in high cost. Further, it causes difficulty in reducing the size of the UV lamp turning-on system, in particular, the high voltage power source.
(3) To enhance the UV light utilization efficiency, a coating forming device has been developed in which a reflection plate equipped with a concave reflection surface is arranged above the upper mold, wherein UV light is irradiated from below the lower mold, the UV light transmitted through the lower and upper molds being reflected by the reflection plate to be condensed on the UV curable resin in the re-coating groove of the upper and lower molds. In this coating forming device, only a part of the UV light is transmitted through the lower mold to reach the upper mold, so that the quantity of reflection light is rather small, which means a substantial improvement in terms of the UV light utilization efficiency can not be expected. Further, the upper surface of the upper mold is covered by the reflection plate arranged above the upper mold, and the visual field for inspecting the interior of the coating forming device is closed, making it impossible to check the way the optical fiber is placed in the coating forming device and the way the mold is filled with UV curable resin. Further, since the reflection surface of the reflection plate is concave, it becomes larger in thickness than a reflection plate with a flat reflection surface, resulting in an increase in the size of the reflection plate, which causes difficulty in reducing the size of the coating forming device.